This invention relates to a device for inspecting the quality of prints in a sheet-feed press, a rotary press and a rewinder.
A variety of print inspecting devices have been proposed in the art. In one of these conventional devices, tone marks or color patches printed in the marginal portions of prints have been inspected to determine the acceptability of the prints. But in the conventional device, the defective portions (such as for instance partially unsatisfactory tones) disappearing in the tone marks or color patches could not be detected, and it is necessary to provide the marginal portions for prints, in which the marks or patches should be printed.
Furthermore, the devices in which data have been obtained from a printed pattern have been also known in the art. In one of the devices, one sensor is used to input the data of the entire area of a pattern printed. In another device, the print area is scanned with a minute spot. But the former device could not detect a large area print with high accuracy, although it was effective in inspecting a small area print such as a brochure. The latter device has taken a lot of time to achieve the data input so that it could not inspect a large area print at high rate.
Furthermore, a comparison system in which a reference data is compared with the next surface data to determine the print acceptability, and a comparison system in which a reference data is compared with the previous inspection data, are known in the art.
However, the former system could not inspect an only-one-image, that is, it cannot be applied to all kinds of prints, and therefore the adjustment was troublesome when the group of print is changed. The latter system could detect positively the defective portions (such as stains due to dripped oil) appearing suddenly in prints, but it could not detect moderate tone change lasting for a long time.